The present invention relates generally to reinforced hydraulic hoses and, more particularly, to hoses which are reinforced with a braided construction.
Heretofore, braided hydraulic hoses have been provided with the reinforcing element being strands of wires braided about the hose tube such as in the illustrations of prior art contained in U.S. Pat. No. 3,463,197 (FIGS. 2A and 3A). The reinforcing element serves to withstand the forces of pressure within the hose and the tube serves to seal the spaces between the strands and the wires of the strands against leakage of the fluid from within the hose. In this construction interstices occur between the braided strands creating open areas in the reinforcement pattern and limiting the maximum operating pressure of the hose. In an attempt to reduce the area of the interstices, and to increase the degree of reinforcement, strands containing more wires have been utilized. However, adding wires to the strands results in more severe crimping of the edge wires in the criss-crossing strands causing the edge wires to rub and to wear more severely under repeated flexing and pressure impulses in the hose. This often results in overstressing and fatigue breakage of the edge wires leading to complete hose failure.
In order to avoid crimping and the resultant wear and breakage problem, to fill up the interstice space, and to increase the degree of reinforcement, utilization of strands composed of a larger number of smaller diameter wires bunched on top of each other in a mound configuration has been proposed in U.S. Pat. No. 3,463,197. While this unconventional construction provides a satisfactory hose, much of the wire utilized in the construction may not be necessary from the strength standpoint. Many lightly stressed underlying wires simply support the wires which are highly stressed in order to reduce crimping and overstressing of the highly stressed wires.
In conventional braided hose reinforcement, all strands are generally flat and each strand follows a twisting, undulating path within the braid pattern travelling over and under the crossing strands. When the strand width exceeds approximately one half the available strand space as wound along the tube, the undulations of the edge wires become greater than the undulations of the central wires resulting in a longer path for the edge wires. The degree of difference between the lengths of the paths of the edge wires and the central wires is determined by the severity of crimping which results as more wires are added to the strand and are forced into path of greater undulations and greater lengths. All wires of the strand are presented to the braid pattern in relatively equal lengths but the edge wires are used up faster in conventional high pressure hoses because their paths are longer and the central wires then tend to slacken. Since the strand is applied under tension, the edge wires see much more than their proportionate share of this tension and the central wires see much less than their share. Likewise, when the hose is pressurized, the edge wires see more than their proportionate share of the operating stresses and the central wires see less than their share. This means the hose cannot be utilized at full strength as would be the case if all wires in the strand were applied at equal tensions and equal lengths and, therefore, more equally shared the stresses of operation.
As the edge wires get tighter and the central wires get looser there is a natural tendency for these wires to seek an equilibrium state by exchanging places. This phenomenon of the central wire crossing above the other wires into the edge position and the other wires moving toward the strand center is practically referred to as a cross-over by the hose industry. Cross-overs have long been felt by the hose industry to be a main point of weakness in a hose and a major cause of hose failure in operation.
Sometimes the cross-over does not occur and the central wire becomes so loose that it entangles in part of the braiding machine and breaks. This causes stopping of the machine and scrapping of the affected length of hose and results in loss of production and in labor expenditure to reconnect the broken wire.
Generally, very high strand application tensions are utilized in braiding high pressure hoses in order to effect the tight crimping of the edge wires and in an attempt to reduce cross-overs and slackness in the central wires. The idea is that, since the slack central wires cannot be shortened, the edge wires must be stretched by high tension so they more nearly equal the length of the central wires. This dictates the use of very strong tube materials, which are expensive, capable of withstanding the high strand tension without deforming or extruding through the braided strands. Also in many cases it is necessary to freeze the tube material to make it hard enough to withstand the strand application tension. Again this is an added expense to the manufacture of the hose.
Furthermore, in the prior attempts to increase the number of wires in each strand in order to reduce the area of the interstices, a bunching effect occurs in which the outermost wires of each strand move in towards the center of the strand displacing the central wires. This opens up the interstices, increasing their areas and reducing the areas of proper reinforcement, and results in an unacceptable hose. This bunching effect occurs in braiding of hoses utilizing strands composed of more than about ten or twelve wires and where the strand is intended to fill more than about eighty percent of the available strand space. Therefore, in conventional high pressure braided hose construction, the hose size dictates the minimum number of strands utilized for its manufacture; larger hoses require more strands and larger braiding mmachines to accommodate the additional strand containers. Increasing the number of strands increases the number of crimp points magnifying the chance of a failure. The larger machines are naturally mmore expensive, produce hose at a slower rate, and require considerable space in the manufacturing plant. The physical size of braiding machines available today results in a limit of about four inches diameter for conventionally constructed high pressure hoses. Hoses of greater size may be made by less desirable methods than braiding and generally do not have as good performance capability or low cost as would a braided hose.
Multiple layers of braided wire have also been utilized to reinforce hydraulic hoses to provide increased strength to the hose. While these hoses have slightly greater pressure capacity, they still basically have the same problems and weaknesses as the single layer reinforcement pattern. The multiple layer hoses are made by passing the hose tube through a series of braider decks where one braided layer is wrapped upon the other usually with an interlayer of rubber between the layers. Successive layers lie farther from the hose axis and therefore, in order to maintain the optimum braid angle at approximately 54 degrees 44 minutes in each layer of the multiple layer constructions, the pitch of the braid's helix is made different for the different braiding decks corresponding to its respective layer's distance from the hose axis so that the braid angle will be approximately the same or about 54 degrees 44 minutes for each braid layer.
Other reinforcement patterns have been utilized for hydraulic hose such as spiral wrapped hose whereby all the wires of a layer are applied in the same helical direction and the wires of successive layers are applied in alternating helical directions. While this eliminates the crimping problem, affords a greater degree of reinforcement, and provides for more equal sharing of the operating stresses among the wires, the hose is not entirely satisfactory for applications where the hose need be highly flexible in operation. Expensive and difficult to make, the spiral wrap reinforced hose also creates problems in retaining the couplings on the hose because no interlocking occurs between the overlapping spiral layers as occurs in braiding. Interlocking of the criss-crossing braid strands prevents unwinding of the strands and helps prevent the coupling from being forced from the end of the hose when the hose is pressurized.
Accordingly, an important object of the present invention is to provide a braid-reinforced hose construction in which crimping is reduced thereby reducing excessive stress on the edge wires.
Another important object of the present invention is to provide a braid reinforced hydraulic hose which has greater coverage of the reinforcing elements or material than can be achieved in conventional braid reinforced hose construction and which, at the same time, reduces the crimping effect.
Still another important object of the present invention is to provide a reinforced hydraulic hose having a braided construction in which increased coverage of the reinforcement pattern occurs without causing bunching of the wires in the strands and without utilizing unstressed wires.
Still another important object of the present invention is to provide a reinforced hydraulic hose having a braided construction in which all wires of a strand are applied at nearly equal tensions and along paths of nearly equal lengths.
Still another important object of the present invention is to provide a reinforced hydraulic hose having a braided construction in which the tension of application of the strands is reduced, permitting the use of softer tube materials and reducing the need for freezing of the tubes.
Still another important object of the present invention is to provide a reinforced hydraulic hose having a braided construction in which all wires of a strand are nearly equally stressed when the hose is pressurized to permit higher operating pressures than conventional hoses and to extend the service life of the hose.
Still another important object of the present invention is to enable braiding of flat strands composed of more wires than is normally possible with conventional constructions.
Still another important object of the present invention is to provide higher coverage without reducing flexibility of the hose or to provide equal coverage while increasing flexibility.
Yet another important object of the present invention is to provide higher coverage while maintaining interlocking of the strands to effect proper coupling retention.